By default any code loaded into something like SBCL gets AOT compiled. In Common Lisp not anything can change at any moment. Especially not in implementations

By default any code loaded into something like SBCL gets AOT compiled. In Common Lisp not anything can change at any moment. Especially not in implementations where one uses AOT compilation like SBCL, ECL, LispWorks, Allegro CL, ... and so on. They have optimizing compilers which gradually can remove dynamic runtime behavior, upto supporting almost no dynamic runtime behavior. Stuff which is supported: type specific code, inlining, block compilation, removal of development tools, ... JIT implementations are rare in the Common Lisp world. They are mostly only used in implementations which use a byte-code virtual machine (CLISP, ABCL, ...). Common Lisp implementations mostly compile either directly to native code or via C compilers. The effect is that native AOT compiled code is much faster.